1. Field of the Invention
This invention relates to an automatic transmission for motor vehicles, which is provided with a plural number of parallel transmission shafts.
2. Description of the Prior Art
There is known in the art an automatic transmission including a first shaft rotatably supported by the automatic transmission case and consisting of an input shaft coupled with the output shaft of the engine through a fluid joint or a friction clutch and an output shaft disposed coaxially in series with the input shaft and mounting thereon a helical output gear; a second shaft consisting of a long shaft rotatably supported by the automatic transmission case parallel with the first shaft and a short shaft mounted on the long shaft, one of the long and short shafts serving as an input shaft having a helical gear connected to the helical output gear on the first shaft by direct meshing engagement therewith or through a chain or an idler gear while the other one serving as an output shaft having a helical output gear; a differential having a large helical drive gear connected to the output gear of the second shaft by direct meshing engagement therewith or through a chain or an idler gear; a first speed-changing planetary gear mechanism provided on the first shaft; and a second speed-changing helical planetary gear mechanism provided on the second shaft. In this sort of automatic transmission, it has been the conventional practice to provide a pair of taper roller bearings on the inner side of the output gear of the second shaft, fitting the input shaft of the second shaft in the inner diameter of the taper roller bearings. This results in a greater reduction ratio and in the increase of the transmitting torque of the second shaft, necessitating to employ taper roller bearings of large capacity to cope with the large radial load and moment which are imposed as a result of transmission of large torque between the output gear of the second shaft and the large drive gear of the differential.